35,431 research outputs found
An experimental SMI adaptive antenna array for weak interfering signals
A modified sample matrix inversion (SMI) algorithm designed to increase the suppression of weak interference is implemented on an existing experimental array system. The algorithm itself is fully described as are a number of issues concerning its implementation and evaluation, such as sample scaling, snapshot formation, weight normalization, power calculation, and system calibration. Several experiments show that the steady state performance (i.e., many snapshots are used to calculate the array weights) of the experimental system compares favorably with its theoretical performance. It is demonstrated that standard SMI does not yield adequate suppression of weak interference. Modified SMI is then used to experimentally increase this suppression by as much as 13dB
Finite self-similar p-groups with abelian first level stabilizers
We determine all finite p-groups that admit a faithful, self-similar action
on the p-ary rooted tree such that the first level stabilizer is abelian. A
group is in this class if and only if it is a split extension of an elementary
abelian p-group by a cyclic group of order p.
The proof is based on use of virtual endomorphisms. In this context the
result says that if G is a finite p-group with abelian subgroup H of index p,
then there exists a virtual endomorphism of G with trivial core and domain H if
and only if G is a split extension of H and H is an elementary abelian p-group.Comment: one direction of theorem 2 extended to regular p-group
Effect of Fibonacci Modulation On Superconductivity
We have studied finite-sized single band models with short range pairing
interactions between electrons in presence of diagonal Fibonacci modulation in
one dimension. Two models, namely the attractive Hubbard model and the
Penson-Kolb model, have been investigated at half-filling at zero temperature
by solving the Bogoliubov-de Gennes equations in real space within a mean field
approximation. The competition between ``disorder'' and the pairing interaction
leads to a suppression of superconductivity (of usual pairs with zero
centre-of-mass momenta) in the strong-coupling limit while an enhancement of
the pairing correlation is observed in the weak-coupling regime for both the
models. However, the dissimilarity of the pairing mechanisms in these two
models brings about notable difference in the results. The extent to which the
bond ordered wave and the -paired (of pairs with centre-of-mass momenta =
) phases of the Penson-Kolb model are affected by the disorder has also
been studied in the present calculation. Some finite size effects are also
identified.Comment: 14 pages, 13 figure
Inelastic scattering of protons from He and Li in a folding model approach
The proton-inelastic scattering from He and Li nuclei are
studied in a folding model approach. A finite-range, momentum, density and
isospin dependent nucleon-nucleon interaction (SBM) is folded with realistic
density distributions of the above nuclei. The renormalization factors N
and N on the real and volume imaginary part of the folded potentials are
obtained by analyzing the respective elastic scattering data and kept unaltered
for the inelastic analysis at the same energy. The form factors are generated
by taking derivatives of the folded potentials and therefore required
renormalizations. The values are extracted by fitting the p +
He,Li inelastic angular distributions. The present analysis of
p + He inelastic scattering to the 3.57 MeV excited state, including
unpublished forward angle data (RIKEN) confirms L = 2 transition. Similar
analysis of the p + He inelastic scattering angular distribution leading to
the 1.8 MeV (L = 2) excited state fails to satisfactorily reproduce the data.Comment: one LaTeX file, five PostScript figure
Stellar Mass to Halo Mass Scaling Relation for X-ray Selected Low Mass Galaxy Clusters and Groups out to Redshift
We present the stellar mass-halo mass scaling relation for 46 X-ray selected
low-mass clusters or groups detected in the XMM-BCS survey with masses
at
redshift . The cluster binding masses are inferred
from the measured X-ray luminosities \Lx, while the stellar masses
of the galaxy populations are estimated using near-infrared imaging from the
SSDF survey and optical imaging from the BCS survey. With the measured \Lx\ and
stellar mass , we determine the best fit stellar mass-halo mass
relation, accounting for selection effects, measurement uncertainties and the
intrinsic scatter in the scaling relation. The resulting mass trend is
, the intrinsic (log-normal) scatter is
, and there is no
significant redshift trend , although
the uncertainties are still large. We also examine within a fixed
projected radius of ~Mpc, showing that it provides a cluster binding mass
proxy with intrinsic scatter of (1 in ). We
compare our scaling relation from the XMM-BCS
clusters with samples of massive, SZE-selected clusters
() and low mass NIR-selected clusters
() at redshift .
After correcting for the known mass measurement systematics in the compared
samples, we find that the scaling relation is in good agreement with the high
redshift samples, suggesting that for both groups and clusters the stellar
content of the galaxy populations within depends strongly on mass but
only weakly on redshift out to .Comment: 15 pages, 10 figures. Accepted for publication in MNRA
Ferromagnetism in the Mott insulator Ba2NaOsO6
Results are presented of single crystal structural, thermodynamic, and
reflectivity measurements of the double-perovskite Ba2NaOsO6. These
characterize the material as a 5d^1 ferromagnetic Mott insulator with an
ordered moment of ~0.2 Bohr magnetons per formula unit and TC = 6.8(3) K. The
magnetic entropy associated with this phase transition is close to Rln2,
indicating that the quartet groundstate anticipated from consideration of the
crystal structure is split, consistent with a scenario in which the
ferromagnetism is associated with orbital ordering.Comment: 5 pages, 5 figures, added reference
Attentive Neural Architecture Incorporating Song Features For Music Recommendation
Recommender Systems are an integral part of music sharing platforms. Often
the aim of these systems is to increase the time, the user spends on the
platform and hence having a high commercial value. The systems which aim at
increasing the average time a user spends on the platform often need to
recommend songs which the user might want to listen to next at each point in
time. This is different from recommendation systems which try to predict the
item which might be of interest to the user at some point in the user lifetime
but not necessarily in the very near future. Prediction of the next song the
user might like requires some kind of modeling of the user interests at the
given point of time. Attentive neural networks have been exploiting the
sequence in which the items were selected by the user to model the implicit
short-term interests of the user for the task of next item prediction, however
we feel that the features of the songs occurring in the sequence could also
convey some important information about the short-term user interest which only
the items cannot. In this direction, we propose a novel attentive neural
architecture which in addition to the sequence of items selected by the user,
uses the features of these items to better learn the user short-term
preferences and recommend the next song to the user.Comment: Accepted as a paper at the 12th ACM Conference on Recommender Systems
(RecSys 18
Electronic Structures, Born Effective Charges and Spontaneous Polarization in Magnetoelectric Gallium Ferrite
We present a theoretical study of the structure-property correlation in
gallium ferrite, based on the first principles calculations followed by a
subsequent comparison with the experiments. Local spin density approximation
(LSDA+U) of the density functional theory has been used to calculate the ground
state structure, electronic band structure, density of states and Born
effective charges. Calculations reveal that the ground state structure is
orthorhombic Pc21n having A-type antiferromagnetic spin configuration, with
lattice parameters matching well with those obtained experimentally. Plots of
partial density of states of constituent ions exhibit noticeable hybridization
of Fe 3d, Ga 4s, Ga 4p and O 2p states. However, the calculated charge density
and electron localization function show largely ionic character of the Ga/Fe-O
bonds which is also supported by lack of any significant anomaly in the
calculated Born effective charges with respect to the corresponding nominal
ionic charges. The calculations show a spontaneous polarization of ~ 59
microC/cm^2 along b-axis which is largely due to asymmetrically placed Ga1,
Fe1, O1, O2 and O6 ions.Comment: Total 21 pages including 3 tables and 6 figure
A study of Feshbach resonances and the unitary limit in a model of strongly correlated nucleons
A model of strongly interacting and correlated hadrons is developed. The
interaction used contains a long range attraction and short range repulsive
hard core. Using this interaction and various limiting situations of it, a
study of the effect of bound states and Feshbach resonances is given. The
limiting situations are a pure square well interaction, a delta-shell potential
and a pure hard core potential. The limit of a pure hard core potential are
compared with results for a spinless Bose and Fermi gas. The limit of many
partial waves for a pure hard core interaction is also considered and result in
expressions involving the hard core volume. This feature arises from a scaling
relation similar to that for hard sphere scattering with diffractive
corrections. The role of underlying isospin symmetries associated with the
strong interaction of protons and neutrons in this two component model is
investigated. Properties are studied with varying proton fraction. An analytic
expression for the Beth Uhlenbeck continuum integral is developed which closely
approximates exact results based on the potential model considered. An analysis
of features associated with a unitary limit is given. In the unitary limit of
very large scattering length, the ratio of effective range to thermal
wavelength appears as a limiting scale. Thermodynamic quantities such as the
entropy and compressibility are also developed. The effective range corrections
to the entropy vary as the cube of this ratio for low temperatures and are
therefore considerably reduced compared to the corrections to the interaction
energy which varies linearly with this ratio. Effective range corrections to
the compressibility are also linear in the ratio.Comment: 39 pages, 15 figures, 2 table
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